There are numerous types of what are referred to as "egg-crate" grids, i.e. having continuous or discontinuous baffles arranged in a rectangular, perpendicular relationship with equal squares surrounded or outlined by adjacent intersecting baffles. The baffles need not be continuous, but merely give the impression of rectangular spaces, two outstanding examples of this type being those of U.S. Pat. No. 3,774,024, in which the grid is formed by individual pieces which overlap laterally to provide light interception but may be turned into straight rows to facilitate cleaning, and U.S. Pat. No. 4,021,985, in which secondary baffles are formed from slots in parallel primary baffles and turned to 90.degree. positions. Arcuate, concave baffles have been proposed, such as parallel rows of concave, transversely arcuate panels between lights, with concave, arcuate panels also extending downwardly on a wall, as in U.S. Pat. No. 4,083,153. A series of inwardly concave elements, relatively short in height, have been proposed as shades for a light, with circular rows of such elements surrounding the light and the radius of the arc increasing for successive rows, as in U.S. Pat. No. 3,736,418. A cellular light control panel, molded of plastic or the like, has intersecting walls which are formed in a tunnel shape, as in U.S. Pat. No. 3,024,355, but the height of each wall, at the intersecting positions, must vary from the center to each edge in order to obtain the same angle of light intersection for each cell. A dome shape is formed by one side of a cellular light control structure, again molded of plastic or the like, in U.S. Pat. No. 3,024,355, but the four outer edges of the structure are in the same plane and again the same variation in height at each intersection of the cellular walls is necessary. As far as is known, there is no dome-shaped grid structure, or one for which illumination is optional, whose outer edges are generally concave or whose intersecting plates may be the same height at each intersection, or a vaulted grid structure whose intersecting plates may be the same height at each intersection.
A principal object of this invention is to provide a vaulted or dome-shaped grid which does not require the formation of a plate into a laterally curved configuration; to provide such a vault grid for which a series of plates may be left in flat or planar condition but be generally concave on one side with the opposite side generally parallel thereto; to provide such a vault grid which may optionally be illuminated, either from above or below, as by light fixtures or even a skylight; to provide such a vault grid which comprises two series of intersecting plates with the height of the plates being substantially the same at each intersection; to provide such a vault grid in which the angle of light cutoff between plates may be made substantially equal for each of the spaces between adjacent plates without affecting the equal heights of the plates at intersections; to provide such a vault grid, the underside of which has a dome shape with the side edges being concave on the dome side; to provide such a vault grid which is supported in such a manner that, when illuminated, access to light fixtures above the grid, is readily obtainable; to provide such a vault grid which may be formed from individual plates capable of being mass produced on a consistent and accurate basis; and to provide such a vault grid which is conveniently and economically manufactured.